The potential for a drug-drug interaction between modafinil and dextroamphetamine, each at steady state, was investigated in an open-label, randomized, single-period studyin 32 healthy male and female volunteers. All subjects received modafinil orally once daily for 28 days (200 mg on Days 1-7; 400 mg on Days 8-28). On Days 22 to 28, half of the subjects also received dextroamphetamine (20 mg) orally 7 hours after modafinil. Samples for pharmacokinetic (PK) profiling were obtained on Days 21 and 28.
The mean changes in PK parameters for modafinil and its two circulating metabolites between the two groups were not statistically significantly different, except Cmax for modafinil acid. Adverse events obtained in the two groups were similar and mild or moderate in nature. The results indicate that administration of low-dose dextroamphetamine in this dosing regimen does not alter the steady-state pharmacokinetics of modafinil. The combination has a similar tolerability profile as modafinil alone.